1. Field of the Invention
The present invention relates to start control in a passenger protection system for achieving protection of passengers in clash of a vehicle and, more particularly, an improvement in the start control for a passenger protection system which intends to protect the passenger by sensing a side clash of the vehicle.
2. Description of the Related Art
In the field of the so-called air bag system which is representative of the passenger protection system, in addition to the air bag system which can protect mainly the passenger from the frontal clash, recently so-called various side air bag systems which can protect the passenger from the side clash of the vehicle have been proposed, and some of them have been employed in practical use.
In most of the side air bag systems which have been proposed up to now in this country, units being called ECUs (Electrical Control Units) for controlling the side air bag system are installed in so-called B pillars provided substantially on the boundary areas between the front doors and the rear doors of the four door vehicle. However, in this manner, in the case of the configuration in which the ECUs are provided in the B pillars, the ECUs are needed so as to correspond to the number of the requested air bag system. For example, if the driver should be protected from the side clash of the driver's seat and simultaneously the passenger should be protected from both side clashes of the rear seat, the ECUs are provided in right and left B pillars respectively. In this case, two ECUs are needed in total. Two ECUs of the side air bag systems are then connected to a unit called a center ECU. Because this center ECU is provided in the center area of the vehicle, for example, cable connection between the center ECU and two ECUs are needed. As a result, such disadvantages are brought about that the configuration becomes complicated and cost of the vehicle becomes higher.
In order to overcome the above disadvantages, it has been examined that the ECUs for a plurality of side air bag systems are arranged at or near the location where the center ECU is arranged (so-called single point arrangement). In such case, various following problems must be overcome.
More particularly, normally the center ECU is often provided near the center area of the vehicle. Therefore, if the ECUs for the side air bag systems are arranged in vicinity of the center ECU, they are positioned remote from the side surfaces of the vehicle. As a result, sensors which are provided together with the ECUs for the side air bag systems to detect the impact acceleration caused by the side clash are also positioned remote from the side surfaces of the vehicle. Thus, the problem has arisen that a detection sensitivity of the impact acceleration is decreased. Hence, the counterplans such that the sensitivity of the sensor per se is increased, the detection sensitivity in the software process by the ECU is increased, etc. are requested.
However, in the event that the sensitivity of the sensor per se is increased, the detection sensitivity in the software process by the ECU is increased, etc., such counterplans cannot be implemented not to bring about new another problems. In other words, enhancement of such detection sensitivity means that the impacts generated due to various causes other than the clash are detected by the acceleration sensor as the impact acceleration.
For example, the impact being caused by so-called underfloor interference (resonance of the floor, etc.) during traveling of the vehicle, the impact being caused by so-called seat slide (movement of the seat), or the like can be caught by the acceleration sensor. Therefore, such a new problem has arisen that there is a possibility that these impacts exceed the threshold value to decide start of the side air bag systems to thus cause the false decision. As a result, a countermeasure to avoid the possibility of such false decision must be further applied.